A Galilean laser beam expander typically includes a single negative focal length lens on the input side and a multi-element positive focal length lens group on the output side. The divergence of a laser beam can be adjusted by changing the focal setting of the output telescope. More specifically, by changing the spacing between the negative input lens and the positive output lenses of the Galilean beam expander, the output telescope collimation and divergence of the output laser beam can be adjusted.
By mounting the lenses in a metal tube wrapped with a heater one could change the telescope focal setting by adjusting the beam expander tube temperature via heater power. However, a relatively large amount of motion (e.g., ˜0.25 mm) may be required to achieve decollimation. One problem with this approach is that it may require a large change in tube temperature (e.g., 75-127° C.) to achieve such a change in spacing. The 0.25 mm spacing and 75-127° C. change in tube temperature are provided by way of example only for a specific beam expander magnification, tube length, and material. These factors will vary from one beam expander design to another. Accordingly, an improved laser beam expander may be beneficial.